Process for preparing 6-bz-1-dibromobenzanthrone



Patented July 4, 1944 PROCESS FOR PREPARING 6-Bz-1- DIBROMOBENZANTHRONE Henry R. Lee, Pitman, and Clarence F. Belcher, Bridgeton, N. J., assignors to E. I. du Pont de Nemours & (lompanm wilmington, Del., a corporation "of Delaware 7 Application November 13, 1942 Serial No. 465,486

I No Drawing.

6 Claims. (91. 260352) This invention relates to. animprovement in the process for preparing (i-B zl d ibromobenzanthrone, and more particularly to a method-for isolating the 6 Bzl dibromobenzanthrone in a state of high purity and in, relatively highyields from the organic solvent in which it is formed. 6 Bz l dibromobenzanthrone, produced by bromination of n n r n or an So nt such as nitrobenzenes, chlorobenzenes, etc, is difiicult to obtain in pure form dueto theformationof substantial amounts'of isomers and partially brominated bodies during the bromination reaction. Wh re t e. df bromo en e ih ne is purified by repeatedly recrystallizingfrom or: an c solventsv s a v v tr be z ne 1, o s de able loss in yield is experienced due to some solubility of the dibromobenzanthrone in the or ganic solvents;

It is therefore an object of the presentinven t on t r v d a sim e and onomica rocess for isolating 6- l3z-l dibromobenzanthrone from the organic solvent in whichit produced, and which will give the 6Bz 1 dibromobenzanthrone ma s d h rity an n sa eness yields. H g, I We. have found, a whenv enzenihrqne i brominated in organic solvents such a 7 nitrobenze e. hl roben cneseet t by th methods disclosed in the Prior art, the 6- Bz ldibromo benzanthrone can be separated from the organic solvent and the normally occurring impuritiesby xtra t n h e d bmQb n at from thesolution with sulfuric acid'of nbin vea to 88% concentration. The extractionjmay .be carried out by running theorganic solvent bromination mass into sulfuric acidof from 78% to 88% strength, orby adding it to concentrated sulfuric acid and 'adjusting theacid concentration so that the sulfuric acid in the mass'islof a concentration from 78% to 88% acid. we'nave found that in sulluric 'acid of. from 78% to 88% strength, the impurities. including the isomeric halogenated compounds, "remain dissolved while the '6 Bz-1-dibromobenzanthrone separates. out asa slurry of reddish-brown crystals whichfappears to be the oxonium 'sulfateof the" 6-32 1- dibromobenzanthrone. The mass is thenfiltered and the oxonium sulfate is hydrolyzedfto the 6-Bz-1-dibromobenzanthr0he with water, preferably during a steam distillation; to remove, any adhered solvent from the filter cake. j- By this process the minimum'amount for solvent can be employed inthe bromination step, because the removal of impurities normally ocinf curring in the resulting bromination mass will not be dependent upon the large excess of solven normally employed, but is, instead, dependent more particularly upon the concentrationof sulfuric acid employedin the extraction step. Th yield of dibromobenzanthrone by this process is, of course, mainly dependent u on 'thevefficiency of the bromination step. By employing sulfuric acid to extract the 6-.Bzl-dibromobenzanthrone, the yield of the desired product in a state of high purity is usually increased because there is less loss of, the desired 6-Bz-l-dibromobenzanthrone in the largeexcess of organic solvent that must otherwise be employed, either in the bromination step or in subsequent recrystallizations that must be carried out where smaller amounts of organic solvent are employed in the bromination reaction.

While the extraction of the fi-Bz-l-dibromobenzanthrone according to the present invention is preferably coupled with the bromination of the benzanthronev by the process more particularly described in U. S. Patent 2,180,835 to Perkins & Deinet, it will be obvious that the process is applicable to other. processes. for brominating benzanthrone in organic solvents. This process is based upon our discovery that the 6-Bz-1-dibromobenzanthrone forms an insoluble compound which appears to be the oxonium sulfate in sulfuric acid of from 78% to 88%, coupled with the fact that the normally occurring impuritiessuch as isomeric dibromo compounds, monobromo compounds and some chlorobromo derivatives, remain soluble in acid of this'concentration or in the organic solvent. It will therefore be obvious, as more particularly illustrated by the following examples, that the dilemmabenzanthrone produced by bromination in organic solvents, can also be purified, after isolationifrom the organic solvent, by slurrying or dissolving the crude brominated filter'cake in concentrated sulfuric "acid' and then reducing the acid concentration to from 78% to 88%. The extraction, however, is preferably caried out prior to isolation of the dibromobenzanthrone from the bromination mass, for to some extent the impurities that are occluded in the dibromobenzanthrone, as it is crystallized from the .organic solvent, are eliminated if thedibromobenzanthrone is extractedfwith the sulfuric acid prior to isolation. The yields are also somewhat increased, because by the combined process less organic solvent need be employed in th bromination step, whereby less dibromobenzanthrone is carried out in solution in the filtrate during the isolation from the solvent.

The following examples are given to illustrate the invention. The parts used are by weight.

Example 1 Following the general procedure of U. S. Patent 2,180,835, 100 parts of benzanthrone are stirred into 300 parts of dry nitrobenzene and heated to 8085 C., at which temperature the benzanthrone is dissolved. Two parts of iodine are added and a mixture of '78 parts of liquid bromine with 65 parts of sulfuryl chloride are added, preferably under the surface, over a period of several hours. When the addition of the brominating agent is complete thereaction mass is maintained on temperature a few hours longer, or until analysis of a sample indicates the introduction of two atoms of bromine into the benzenthrone molecule. The warm reaction massis then dropped directly into a vented vessel containing 1000 parts of 82.5i0.5% sulfuric acid heated at 100i5 C.. After stirring for one-half to one hour at 100:5 C., the charge is cooled to 2530. Microscopic inspection shows reddishbrown-needle-like crystals. The cooled charge is filtered on a stone or carborundum filter and the crystalline residue washed with 82% sulfuric acid. The reddish-brown residue is hydrolyzed in hot water to a bright greenish-yellow precipitate which is filtered off, washed free from acid and dried. The 6-Bz-l-dibromobenzanthrone thus obtained, although it contains traces of chlorine, is of relatively high purity, having a melting point of 257-258 C. 1

Example 2 100 parts of benzanthrone in 400 parts of dry orthodichlorobenzene are stirred and heated at 8085 C. Two parts of iodine are-added and then a mixture of '78 parts of liquid bromine and 65 parts of sulfuryl chloride are slowly added under the surface of the charge over a four hour period while maintaining the temperature at 80- 85 C. Stirring and heating are continued an addition-a1 sixteen hours. The warm reaction mass is poured into. 1000 parts of 83% sulfuric acid .heated .at 90 C. After stirring one-half hour at 90-100 C., the charge is cooled to ordinary temperature and filtered on a carborundum plate. The residue .is Washed with 83% sulfuric acid and then. hydrolyzed. in hot water. The resultant greenish-yellowcrystalline product is 6- Bz-l-dibromobenzanthrone ofhigh urity, melting at 257 258 C.

Example 3 50 parts of pure benzanthrone are covered With 250 parts of liquid bromine according to the disclosure of British Patent 20,837/06 and allowed to stand twenty-four hours. The nearly solid mass is loosened and partly dissolved by adding 200 parts of nitrobenzene' and warming at 80- 85 C. The warm mass is poured into 500 parts of 82.5% sulfuric acid heated at 100 C. for one hour. The charge is cooled to room temperature and filtered on stone or carborundum. The residue is washed with 250 parts of 82.5% H2804, then hydrolyzed in hot water. The yellow crystalline product is 6-Bz-l-dibromobenzanthrone of high purity, having a melting point of 259- 259.5 C. It contains 42% bromine.

Example 4 To a mixture of 250 parts of dry nitrobenzene, 100 parts of pure benzanthrone and 2 parts of iodine, stirred and heated at 80 0., there is added a mixture of 78 parts of liquid bromine with 65 parts of sulfuryl chloride over eight to ten hours. The reaction mass is maintained at C. for an additional eight hours and then dropped into 860 parts of 96% sulfuric acid. This solution is warmed to -100 C. and diluted gradually with parts of water at that temperature, reducing the sulfuric acid content to 83%. Large reddish-brown needle-like crystals are formed. The charge is cooled and filtered on stone or carborundum and the reddish-brown crystallized residue is washed with 500 parts of 82% sulfuric acid. The residue is hydrolyzed in hot water in the presence of a small amount of alkaline bisulfite. The hydrolysis is preferably carried out in a steam still in order to recover a small portion of nitrobenzene in the cake. The 6-Bz-l-dibromobenzanthrone thus obtained melts at 258 -259 C.

Example 5 100 parts of crude dry dibromobenzanthrone, prepared according to the method" of British Patent 20,83'7/ 06 orU. S. Patent'2',-180,835, is dissolved in 1000 parts of 93% sulfuric-acid while warming to '75 80 C. The solution is gradually diluted with parts of water while letting the temperature rise to 10015 C. and then maintaining this temperature until dilutionis complete. After cooling to ordinary temperature, the slurry of reddish-brown crystalline material is filtered on stone and washed with 500 parts of 84. 5 :0.5%' sulfuric acid. The residue-is hydrolyzed in wa-' ter to give 6-Bz-1-dibremohenzanthrone melting at 258 -259 C. a a

The use ofsulfuric acid, as described above, provides a simple and economical process for the isolation of G-Bz-l-dibromobenzanthrone of high purity. While sulfuric acid of a'ocncentration above 88% maybe used, it tends to decrease the yields obtained due to the increasingselubility of the desired (i- B-z-l-dibromobenzanthronein higher strength acid. The useof loveerconcentrations than '78%-tends to precipitate out undesirable lay-products and-thereby give a less pure 6-Bz-l-dibromobenzanthrone. While the limits of acid concentrations are therefore not-sharp, the preferred concentrations which have'been found to give high yields of the B-Bz-l-dibromm benzanthrone of high purityare those from 78% to 88%. v

The process notonly'obviates the use of the expensive and less readily available organic solvents, but it permits the separation of 6-Bz l-dibromo benzanthrone from the organic solvents in which it is formed with little loss-of the fi-Bz l-dibremm benzanthrone, and permits this product to be obtained in exceptionally high purity. It will be noted in the above examples that the products obtai red have a melting point even slightry higher than that listed in the'literature for pure fi-Bzaldibromobenzamtln'one. The process-not only permits the use of less expensive-materials in the purification step, but materially reduces the operating time and costs in avoiding'the laborious solvent extractions heretofore'emplo'yed in '-t-he"purifi'cation of this "product. J

'1. In the process for preparmg-fi-Bz-i-uimm mobenzanthrone wherein the crude lorommatron product is suspended in anorganic solvent, the steps which comprise extracting" the organic sol-- vent suspension pf the crude =6-Bz-1-dibromobenzanthrone with'sulftn'ic acid-of from 78% to 88% concentration, filtering the organic solventsulfunfc acid slurry and hydrolyzing the resulting insoluble reddish-brown crystalline residue with water.

2. In the process for preparing fi-Bz-l-dibromobenzanthrone wherein benzanthrone is brominated in an inert organic solvent, the steps which comprise extracting the organic solvent suspension of the crude fi-Bz-l-dibromobenzanthrone with sulfuric acid of from 78% to 88% concentration, filtering the organic solvent-sulfuric acid slurry and hydrolyzing the resulting insoluble reddish-brown crystalline residue with water.

3. In the process for preparing fi-Bz-l-dibromobenzanthrone wherein benzanthrone is brominated in an inert organic solvent, the steps which comprise isolating the fi-Bz-l-dibromobenzanthrone from the bromination mass by extracting the mass with sulfuric acid of from 78% to 88% strength, filtering, washing the filter cake with sulfuric acid of from 78% to 88% strength and hydrolyzing the resulting insoluble reddishbrown crystalline residue by slurrying it in hot water, filtering the resulting fi-Bz-l-dibromobenzanthrone and Washing it acid-free with water.

4. The process for preparing 6-Bz-l-dibromobenzanthrone which comprises reacting benzanthrone in an organic solvent with suflicient bromine to effect dibromination of the benzanlecularly equivalent to the bromine employed, ex-

tracting the bromination mass with sulfuric acid of from 78% to 88% strength, filtering off the resulting insoluble reddish-brown crystalline residue and hydrolyzing the same with water to give the 6-Bz-l-dibromobenzanthrone in a state of high purity.

5. In the process for preparing 6-Bz-l-dibromobenzanthrone wherein benzanthrone is brominated in an inert organic solvent, the steps which comprise extracting the organic solvent suspension of the crude fi-Bz-l-dibromobenzanthrone with sulfuric acid of from 82% to 85% concentration, filtering the organic solvent-sulfuric acid slurry and hydrolyzing the resulting insoluble reddish-brown crystalline residue with water.

6. In the process for preparing 6-Bz-1-dibromobenzanthrone of relatively high purity, the steps which comprise extracting the crude 6-Bz-1- dibromobenzanthrone with sulfuric acid of from 78% to 88% strength, and isolating the resulting insoluble reddish-brown crystalline 6-Bz-1- dibromobenzanthrone sulfuric acid addition product and hydrolyzing it with water.

HENRY R. LEE. I CLARENCE F. BELCHER. 

